A semiconductor device is known in which a semiconductor chip is mounted on a lead frame and encapsulated by resin. Expansion and contraction are repeatedly applied on such a semiconductor device due to the heat generated when being operated. Thus, there is a risk that delamination occurs between an interface of the lead frame and the resin. In order to improve the adhesion between the lead frame and the resin, a bumpy portion may be formed at a surface of the lead frame. For example, the bumpy portion is formed at the surface of the lead frame by chemically roughing the surface of the lead frame.
Patent Document 1: Japanese Laid-open Patent Publication No. 2004-349497
However, according to the method of forming the bumpy portion by chemically roughing the surface of the lead frame, the bumpy portion is finely formed and the surface area is not large enough to obtain the expected adhesion. Further, for example, there is a case that such a bumpy portion is formed by chemically roughing a lead frame made of copper. In such a case, a silver plating film may be formed on the formed bumpy portion. However, the finely formed bumpy portion may be filled by the silver plating film and the surface area may decrease after forming the silver plating film. In such a case as well, the expected adhesion cannot be obtained.